1. Field of the Invention
The present invention relates to a fuel supply device for a fuel returnless system that supplies an internal combustion engine (hereinafter also referred to simply as the engine) with fuel in a fuel tank mounted mainly in a vehicle such as an automobile. In this specification, the fuel returnless system refers to a system that is constructed so as to treat a surplus of fuel in the fuel tank and prevent it from returning from the engine side to the fuel tank.
2. Description of the Related Art
A known fuel supply device for a fuel returnless system of this kind will be described. As shown in FIG. 10, a fuel supply device in a return system is disposed within a fuel tank 101 and is constructed as a module including a fuel pump 110, a high-pressure filter 112, a pressure regulating valve 114, and an intake filter 116.
The fuel pump 110, which is a motorized pump of an in-tank type, draws fuel from a reserve cup 103 installed in the fuel tank 101 through the intake filter 116, pressurizes the fuel, and discharges the fuel to the high-pressure filter 112. The high-pressure filter 112 removes foreign matters contained in pressurized fuel discharged from the fuel pump 110 and discharges the pressurized fuel to the pressure-regulating valve 114. The pressurized fuel will also be referred to hereinafter as “high-pressure fuel”.
The pressure regulating valve 114 regulates the pressure of the pressurized fuel discharged from the high-pressure filter 112 and discharges a surplus of pressurized fuel into the reserve cup 103 through a pressurized fuel return pipe 118. The pressurized fuel whose pressure has been regulated by the pressure-regulating valve 114 is discharged to a fuel supply passage 105 outside the fuel tank 101. The fuel supply passage 105 leads to injectors via a delivery pipe of an engine (not shown). The intake filter 116 removes foreign matters contained in fuel drawn into the fuel pump 110 from the interior of the reserve cup 103.
In the fuel supply device in the aforementioned fuel returnless system, when the fuel pump 110 is driven, fuel within the reserve cup 103 is drawn through the intake filter 116, pressurized, and discharged into the high-pressure filter 112. Fuel that has passed through the high-pressure filter 112 is supplied to the fuel supply passage 105 via the pressure-regulating valve 114. The fuel supplied to the fuel supply passage 105 is supplied to the injectors via the delivery pipe of the engine. FIG. 11 shows how fuel flows in a known fuel supply device (see FIG. 10).
Referring to FIG. 11, “QE” represents an amount of fuel passing through the intake filter 116, that is, an amount of fuel supplied to the engine or a fuel consumption amount at the engine. “QR” represents the amount of a surplus of pressurized fuel (a so-called surplus fuel amount) drained from the pressure-regulating valve 114. “P” represents the pressure in the fuel tank 101, which is equal to the atmospheric pressure when P=0. “PSYS” represents the pressure of the pressurized fuel supplied into a pipeline of an injector or a high-pressure pump provided in a direct injection engine, that is, a so-called system fuel pressure (more specifically, 300 to 600 kPa). “−ΔP” represents a pressure (negative pressure) in the intake filter 116 generated by drawing fuel via the fuel pump 110.
The fuel supply device in the fuel returnless system as described above is disclosed in, for example, JP 9-32672 A.
In the aforementioned fuel supply device, the intake filter 116 provided on the intake side of the fuel pump 110 presents at least some passage resistance (referred to also as “intake resistance”). Thus, a negative pressure environment is created in the intake filter 116 due to a suction force generated by the fuel pump 110 to draw fuel. Accordingly, for example, in the case where fuel containing low-boiling components such as alcohol or the like is used, the low-boiling components contained in the fuel are decompressed and boiled at a high temperature, in a low-pressure environment, etc., so that steam bubbles or vapors v (see FIG. 10) are generated. The fuel pump 110 draws in the vapors v, which may cause a decrease in the flow rate of fuel discharged from the fuel pump 110 and consequently from the fuel supply device.